Method for detecting steady-state and transient air flow conditions for cam-phased engines

ABSTRACT

A particulate filter regeneration method for an internal combustion engine system is provided. The method includes: receiving an outlet temperature signal corresponding to a temperature at an outlet of a particulate filter; receiving an oxygen signal corresponding to an oxygen level in exhaust flowing from said particulate filter; and controlling at least one of airflow and fuel based on said oxygen level such that said outlet temperature is within a desired range.

FIELD OF THE INVENTION

The present invention relates to vehicle engine systems, and moreparticularly to detecting a state of air flow delivered to a cylinder ofan engine.

BACKGROUND OF THE INVENTION

Engines combust a mixture of air and fuel (air/fuel) to drive a pistonin a cylinder. The downward force of the piston generates torque. Athrottle controls air flow delivered to the cylinders. By determiningthe amount of air ingested by the cylinders, the fuel mass can becalculated and a proper air/fuel mixture can be delivered to thecylinders to obtain the desired air-fuel ratio and torque.

Air flow delivered to the cylinders can be measured using a mass airflow (MAF) sensor. The MAF sensor measures the air flow across thethrottle. During steady-state air flow conditions, the air flow measuredacross the throttle provides an accurate estimation of the fresh airflow delivered to the cylinders. Because the MAF sensor measures airflow across the throttle and not the air into the cylinders, it is mostaccurate during steady-state conditions, and is less accurate duringtransient conditions (e.g., when additional air must flow across thethrottle to increase the manifold absolute pressure (MAF), or when themass of airflow must be reduced to reduce the MAF).

Air flow can be estimated using a speed density calculation, which istypically based on MAF, engine RPM, as well as intake air temperatureand pressure. The speed density calculation is only an approximationthat is valid as tong none of the parameters that are not explicitlyaccounted for in the calculation varies. However, because the notaccounted for parameters do vary over a period of time while driving thevehicle, the speed density calculations are only accurate for a shortperiod of time and need to be adjusted over time. In order to maintainthe accuracy of the speed density calculations during transientconditions, the MAF sensor is used during stead state conditions tocorrect speed density calculation.

In engines without variable cam phasing (VCP) or variable cam timing(VCT), if the mass of fresh air entering the cylinder changes (i.e., istransient) there is a corresponding increase or decrease in MAF. Thisindicates that the mass of air is either being accumulated or depletedin the intake manifold. During such transient conditions, the speeddensity calculation is used to determine the mass air flow entering thecylinders. The determination of whether the mass air flow issteady-state or transient can be made by means such as that described incommonly assigned U.S. Pat. No. 5,423,208, the disclosure of which isincorporated herein by reference. The control module uses theappropriate method of estimating the mass air flow into the cylinderbased on the air flow state.

However in engines with VCP or VCT, changes in cam position can occurwithout changing the MAF while causing the MAF sensor reading to changeby a large amount. This occurs because the VCP or VCT system allowsvarying amounts of residual exhaust gas back into the intake manifold,which replaces the fresh air mass in the manifold. As a result, more orless air flows through the throttle and the air flow is transient.Traditional air flow transient/steady-state detection methods, like thatdisclosed in U.S. Pat. No. 5,423,208 will see no change in MAF andincorrectly determine that the air flow is steady-state.

SUMMARY OF THE INVENTION

Accordingly, the present invention provides an air flow statedetermining system that determines a mass air flow into a cylinder of anengine having a cam phaser. The system includes a first module thatdetermines whether an air flow state is one of steady-state andtransient based on a cam phaser position. A second module determines themass air flow using one of a mass air flow sensor signal and a speeddensity relationship based on whether the mass air flow state is one ofsteady-state and transient.

In other features, the system further includes a third module thatprocesses the cam phaser position using a first order linear model andcalculates an updated intermediate value based on a cam phaser position.The air flow state corresponding to cam phaser motion is determinedbased on the updated intermediate value. The air flow state isdetermined based on a difference between the updated intermediate valueand a previous intermediate value.

In another feature, the system further includes a filter module thatfilters the cam phaser position.

In yet other features, the system further includes a dead-band modulethat adjusts the cam phaser position based on a calibrated offset. Thesystem further includes a minimizing module that minimizes the camphaser position to zero if the adjustment results in the cam phaserposition being less than zero.

Further areas of applicability of the present invention will becomeapparent from the detailed description provided hereinafter. It shouldbe understood that the detailed description and specific examples, whileindicating the preferred embodiment of the invention, are intended forpurposes of illustration only and are not intended to limit the scope ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIG. 1 is a functional block diagram of an engine system regulatingusing the air flow state detection control in accordance with thepresent invention;

FIG. 2 is a flowchart illustrating exemplary steps executed by the airflow state detection control according to the present invention; and

FIG. 3 is a functional block diagram of exemplary modules that executethe air flow state detection control of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description of the preferred embodiment is merelyexemplary in nature and is in no way intended to limit the invention,its application, or uses. For purposes of clarity, the same referencenumbers will be used in the drawings to identify similar elements. Asused herein, the term module refers to an application specificintegrated circuit (ASIC), an electronic circuit, a processor (shared,dedicated, or group) and memory that execute one or more software orfirmware programs, a combinational logic circuit and/or other suitablecomponents that provide the described functionality.

Referring now to FIG. 1, an engine system 10 is schematicallyillustrated. The engine system 10 includes an engine 12 that combusts anair and fuel (air/fuel) mixture to produce drive torque. Air is drawninto an intake manifold 14 through a throttle 15. The throttle 15regulates mass air flow (MAF) into the intake manifold 14. The positionof the throttle 15 is adjusted based on a signal from a pedal positionsensor 16 indicative of a position of an accelerator pedal 17. Air isdrawn into a cylinder 20 of the engine through an intake valve 18.Although four cylinders 20 are illustrated, it can be appreciated thatthe engine system 10 can include, but is not limited to, 2, 3, 4, 5, 6,8, 10 and 12 cylinders.

The air is mixed with fuel and is combusted within the cylinder 20 toreciprocally drive a piston (not shown) within the cylinder, whichrotatably drives a crankshaft 24. Exhaust is exhausted from the cylinderthrough an exhaust valve 19 and into an exhaust manifold 25. A fuelinjector (not shown) injects the fuel that is combined with the air. Thefuel injector can be an injector that is associated with an electronicor mechanical fueling system, or another system for mixing fuel withintake air. The amount of fuel injected by the fuel injector isregulated based on the mass air flow into the cylinder 20 to deliver adesired air/fuel ratio.

The opening and closing of the intake and exhaust valves 18, 19 areregulated by an intake camshaft 22 and an exhaust camshaft 23,respectively. The crankshaft 24 rotatably drives intake and exhaustcamshafts 22, 23 using a chain/belt and pulley system (not shown) toregulate the timing of the opening and closing of the intake and exhaustvalves 18, 19, with respect to a piston position within the cylinder 20.Although a single intake camshaft 22 and a single exhaust camshaft 23are illustrated, it is anticipated that dual intake camshafts and dualexhaust camshafts may be used.

An intake cam phaser 26 and an exhaust cam phaser 27 vary an actuationtime of the intake and exhaust camshafts 22, 23, respectively, whichmechanically actuate the intake and exhaust valves 18, 19. Morespecifically, the rotational position of the intake and exhaust camshafts 22, 23 can be advanced and/or retarded relative to a position ofthe piston within the cylinder 20 to vary the actuation time of theopening and/or closing of the inlet and/or exhaust valves 18, 19. Inthis manner, the timing and/or lift of the intake and the exhaust valves18, 19 can be varied with respect to one another and/or with respect toa location of the piston within the cylinder 20.

Adjustment of the intake and exhaust camshafts 22, 23 using the intakeand/or exhaust cam phasers 26, 27 can affect the MAF. For example, whenthe cam phasers 22, 23 are adjusted to increase air delivered to thecylinders 18, less exhaust residual flows into the intake manifold 14displacing less fresh air mass. As a result, the mass of combustible airincreases. Conversely, the intake and exhaust cam phasers 26, 27 can beadjusted to reduce air delivered to the cylinders 20>while increasingthe exhaust gas residual entering the intake manifold 14. As a result,there is more air mass entering the intake manifold 14 and hence thecylinder 14.

When the intake and/or exhaust cam phasers 26, 27 remain in a constantposition, the actuation timing of the intake and exhaust valves 18, 19remains constant. As a result, steady-state air flow occurs and aconstant amount of air is delivered to the cylinders 20. However, whenthe intake and/or exhaust cam phasers are adjusted, the actuation timingis correspondingly adjusted and the amount of air delivered into thecylinder 20 either increases or decreases. The resulting sudden changein air flow is typically referred to as an air transient. An airtransient that results from a change in the camshaft position typicallyexists whenever the intake and/or exhaust cam phasers 26, 27 are movedfrom a fixed position.

The engine system 10 further includes an air flow sensor 30, an enginespeed sensor 31, cam phaser position sensors 32, 33, an intake manifoldair temperature sensor 34 and a MAF sensor 35. A control module 36receives the signals generated by the various sensor and regulatesoperation of the engine system 10 based on the air flow state detectionsystem of the present invention. The air flow sensor 30 measures anamount of air flowing through throttle 15 and the engine speed sensor 31is responsive to the rotational speed of the engine 12. The intakemanifold temperature sensor 34 measures an air temperature within theintake manifold 14 and the MAF sensor 35 measures the MAF within theintake manifold 14.

The cam phaser position sensors 32, 33 are coupled to the intake camphaser 26 and the exhaust cam phaser 27, respectively, and areresponsive their respective rotational positions. When the rotationalposition of the intake and the exhaust cam phasers 26, 27 is adjusted,the cam phaser rotational sensors 32, 33 output a position signal to thecontrol module 36. The position signals can be filtered prior to beingreceived by or within the control module 36 using a first order lagfilter to remove any high frequency noise that may exist.

Airflow transients can occur due to changes that a traditional air flowtransient/steady state detector can detect as well as changes in the camphaser 26,27 position, which the traditional transient/steady statedetector does not detect. Accordingly, the air flow state detectioncontrol of the present invention detects whether the mass air flow is ina steady-state or a transient state based on a signal from a traditionaltransient/steady state detection control and further based on therotational velocity of the cam phasers 26, 27. Furthermore, the controlmodule 36 determines the mass air flow into the cylinders 20 based onwhether the mass air flow is deemed steady-state or transient.

Although the air flow state detection control detects steady-state airflow and/or transient air flow based on the intake cam phaser 26 and/orthe exhaust cam phaser 27 rotational velocities, the air flow statedetection control will be based on the rotational velocity of the intakecam phaser 26 alone being used to detect a steady-state air flow and/ortransient air flow.

At each intake reference pulse, which is based on the engine RPM sensorsignal, the air flow state detection control determines the intake camposition (θ_(ICAM)) based on the intake cam position sensor signal.θ_(ICAM) can be filtered using a first order lag filter (e.g.,y=ay+(1−a)x). Proper selection of the filter coefficient (a) enablessuccessful sampling as slow as every other intake reference pulse. Theair flow state detection control subtracts a calibrated offset (θ_(THR))from the filtered θ_(ICAM) to remove a dead-band associated withθ_(ICAM) (i.e., a cam phaser adjustment value that does not affect MAF).If the difference is less than 0, θ_(ICAM) is set it to 0).

The air flow state detection control inputs θ_(ICAM) into a first ordermodel, which is provided by the following equation:

X(k+1)=αX(k)+βθ_(ICAM)

where X is an intermediate variable, k is the current event and isincremented each intake reference event, and α and β are pre-determinedmodel or filter coefficients. α and β are determined using variousoptimization techniques, such that the following relationship isminimized:

|[X(k)−X(k−1)]−MAF(k)−MAF(k−1)]

where MAF(k)−MAF(k−1) is the change in intake manifold pressure due toonly a change in intake cam position. If the following relationship istrue:

|X(k)−X(k−1)|>Δ_(THR)

the mass air flow is transient and a transient flag is set. Otherwise,the mass air flow is steady-state and a steady-state flag is set.

If the steady-state flag is set, the control module 36 operates in asteady-state mode and estimates cylinder mass air flow based on the airflow sensor 30. If the transient flag is set, the control module 36estimates air flow based on the speed density approach according to thefollowing equation:

$\begin{matrix}{m_{a} = \frac{\eta_{v}V_{d}P_{m}}{{RT}_{o}}} & (1)\end{matrix}$

where m_(a) is mass air into the cylinder, R is the universal gasconstant, V_(d) is the displacement volume of the engine 12, η_(v) isthe volumetric efficiency of the engine 12. T_(i) is the temperature ofthe air delivered into the intake manifold 14 and P_(m) is the intakemanifold pressure. Since R and V_(d) are constants for a given engine,the volume of the engine 12 can be defined according to the followingequation:

$\begin{matrix}{V_{d} = {\eta_{v}\frac{V_{d}}{R}}} & (2)\end{matrix}$

Substituting V_(e) into equation (1), mass of air into the cylinder 20can be defined according to the following equation:

$\begin{matrix}{m_{a} = {\frac{V_{e}}{T_{i}}P_{m}}} & (3)\end{matrix}$

Referring now to FIG. 2, a flowchart illustrates exemplary stepsexecuted by the air flow state detection control. In step 200, controldetermines θ_(ICAM). In step 202, control filters θ_(ICAM) to provide afiltered θ_(ICAM). In step 204, control subtracts θ_(THR) from θ_(ICAM)to remove the dead-band around the parked position. Control determineswhether θ_(ICAM) is less than zero in step 206. If θ_(ICAM) is less thanzero, control continues in step 208. If θ_(ICAM) is not less than zero,control continues in step 210. In step 208, control sets θ_(ICAM) tozero.

Control updates the intermediate variable X(k+1) in step 210. In step212, control determines whether the absolute value of the differencebetween X(k+1) and X(k) is greater than Δ_(THR). If the absolute valueof the difference between X(k+1) and X(k) is greater than Δ_(THR),control continues in step 214. If the absolute value of the differencebetween X(k+1) and X(k) is not greater than Δ_(THR), control continuesin step 216. In step 214, control sets the transient flag and estimatesthe cylinder mass air flow using the speed density approach in step 218.In step 216, sets the steady-state flag. In step 219, control determineswhether the traditional or standard transient/steady state detectioncontrol has indicated that the air flow is steady state (SS) by settinga SS flag. If the SS flag is set, control estimates the cylinder massair flow using the MAF sensor 30 in step 220. If the SS flag is not set,control continues in step 218. In step 222 control sets X(k) equal toX(k+1) and control ends.

Referring now to FIG. 3, exemplary modules that execute the air flowstate detection control will be described in detail. The exemplarymodules include a filter module 300, a dead-band module 302, a θ_(ICAM)minimizing module 304, an X updating module 306, a summer 308, anabsolute value module 310, a comparator module 312 a flag module 314 anda cylinder MAF estimating module 316. The filter module 300 and thedead-band module 302 respectively filter and remove the dead-band valuefrom θ_(ICAM).

The θ_(ICAM) minimizing module 304 caps the minimum value of θ_(ICAM) tozero, if θ_(ICAM) is less than zero after the dead-band removaloperation. The X updating module 306 determines X(k+1) based on X(k),θ_(ICAM) and the first order linear model described in detail above. Thesummer 308 determines the difference between X(k+1) and X(k) and theabsolute value module 310 generates the absolute value of thedifference.

The comparator module 312 compares the absolute value of the differenceto Δ_(THR) and outputs a first signal (e.g., 1) if the difference isgreater than Δ_(THR), and outputs a second signal (e.g., 0) if thedifference is less than Δ_(THR). The flag module 314 sets thesteady-state or transient flag based on the output of the comparatormodule 312. The cylinder MAF module 316 determines the cylinder MAFbased on either the MAF sensor signal or the speed density calculationdepending on the output of the comparator module 312 and the conditionof the standard SS flag.

Those skilled in the art can now appreciate from the foregoingdescription that the broad teachings can be implemented in a variety offorms. Therefore, while this invention has been described in connectionwith particular examples thereof, the true scope of the invention shouldnot be so limited since other modifications will become apparent to theskilled practitioner upon a study of the drawings, the specification andthe following claims.

1. A system for controlling regeneration of a particulate filter, comprising: an outlet temperature sensor that senses a temperature at an outlet of the particulate filter and that generates a temperature signal based on said outlet temperature: an air fuel sensor that senses an oxygen level in exhaust flowing from the particulate filter and generates an oxygen signal based on said oxygen level; and a control module that receives said outlet temperature signal and said oxygen signal and controls regeneration of said particulate filter based on said outlet temperature signal and said oxygen signal.
 2. The system of claim 1 wherein said temperature sensor senses a substrate temperature at said outlet of said particulate fitter.
 3. The system of claim 1 wherein said temperature sensor senses a gas temperature flowing through said outlet of said particulate filter.
 4. The system of claim 1 wherein said control module controls at least one of airflow and fuel to maintain a desired oxygen level in said exhaust, wherein said desired oxygen level is defined by a control band, and wherein said control band is defined by a plurality of selectable ranges for a plurality of selectable temperatures.
 5. The system of claim 4 wherein said selectable temperatures are between five hundred and nine hundred degrees Celsius and said selectable ranges are between zero and ten percent oxygen.
 6. The system of claim 1 wherein said control module estimates an accumulation of soot in said particulate filter and controls regeneration based on said estimation.
 7. The system of claim 6 further including an inlet exhaust temperature sensor that senses a temperature of exhaust flowing into said particulate filter and generates an exhaust temperature signal based on said temperature of exhaust flowing into said particulate fitter and wherein said control module initiates regeneration by commanding engine operation such that said exhaust temperature flowing into said particulate filter is above a soot light-off threshold.
 8. The system of claim 1 wherein when said temperature signal indicates a temperature above a selectable threshold, said control module controls regeneration based on said oxygen signal and said temperature signal.
 9. The system of claim 8 wherein said threshold is five hundred degrees Celsius.
 10. A particulate filter regeneration method for an internal combustion engine system, comprising: receiving an outlet temperature signal corresponding to a temperature at an outlet of a particulate filter, receiving an oxygen signal corresponding to an oxygen level in exhaust flowing from said particulate filter; and controlling at least one of airflow and fuel based on said oxygen level such that said outlet temperature is within a desired range.
 11. The method of claim 10 further comprising estimating an accumulation of soot in said particulate filter and wherein said step of controlling is performed if said estimated accumulation exceeds an accumulation threshold.
 12. The method of claim 11 further comprising receiving a temperature signal corresponding to an inlet temperature of said particulate filter and controlling at least one of airflow and fuel to said engine such that said inlet temperature is above a soot light-off threshold when said estimated accumulation exceeds an accumulation threshold.
 13. The method of claim 10 wherein said receiving comprises receiving an outlet temperature signal corresponding to a temperature of particulate filter substrate at said outlet of said particulate filter.
 14. The method of claim 10 wherein said receiving comprises receiving an outlet temperature signal corresponding to a temperature of gases flowing from said outlet of said particulate filter.
 15. The method of claim 10 wherein said desired range for said outlet temperature is between five hundred and nine hundred degrees Celsius.
 16. The method of claim 10 wherein said oxygen level is controlled to be within a desired range for a given outlet temperature.
 17. The method of claim 16 wherein said desired range for said oxygen level is between zero and ten percent oxygen.
 18. The method of claim 10 wherein said step of controlling at least one of airflow and fuel based on said oxygen level continues as long as soot is available to be burned. 